The present invention relates to a plastic fence construction which allows rapid and simple assembly while providing a strong and impact resistant construction utilizing members extruded from polyvinyl acetate or other similar material.
Fences have long been used for both utilitarian and decorative purposes, using wood as the primary material because of low cost, ease of handling, and because it gives a desirable sense of size and strength as compared to metal. The most common way of constructing such a fence is to use a number of wooden posts placed in the ground at regular spaced intervals. Lower and upper rails are then placed horizontally between the posts and fastened to them, and then boards or spindles are positioned vertically, either between the rails or, if greater height is desired, along the sides or through openings in the rails to extend above the top rail. Depending upon the application and cost of the fence, many variations in the finished design are possible, and many of these have achieved such a high degree of acceptance that they have become well known in the trade.
However, wood has many disadvantages, such as being relatively heavy for a given strength, as well as splitting and breaking under impact. Furthermore, wood will tend to rot and decay under most conditions and must be protected either by a preservative finish using an expensive chemical treatment or else painted with appropriate decorative finishes which must be reapplied periodically. Thus the complete cost of a wood fenced is not only the original cost of erecting it, but also the continuing cost of maintenance and repair.
In order to overcome the problems with wood as a fencing material, a number of substitutes have been proposed, particularly plastics, and of these polyvinyl chloride or PVC has been one of the most popular. PVC has the advantages of easy fabrication by extrusion, molding and other processes, as well as reasonable cost and durability, since it can easily be coated with the necessary protective and finishing materials.
Since PVC has approximately three times the density of a typical wood used for fencing, and because of its much higher strength, it is generally formed in hollow extrusions that are shaped to resemble wood boards and posts that essentially are hollow, with walls thick enough to provide the necessary strength and an open center core. In some cases, a core may be filled with wood, usually in the case of posts, for greater strength, and to allow external hardware, such as hinges and latches, to be attached using ordinary screws and bolts. In the case of elongated boards, however, the high width-to-thickness ratio requires the use of internal walls, generally running perpendicular to the long sides and parallel with the end walls, to provide the necessary rigidity. While this arrangement tends to be sufficient for the boards that may be used in either a horizontal or vertical position, fence structures with vertical boards are often used for privacy purposes where the boards are abutted edgewise in a generally vertical position and are supported on top and bottom rail members which extend horizontally between the posts. This arrangement requires rail members to be formed of substantially heavier material to take the weights of the intervening boards and other loads and, from a point of cost and structural strength, it has generally been found desirable to use rail members having the internal cross walls and also a suitable steel channel member in the central portion, not only to provide beam strength, but also, in some cases, to receive suitable screw fasteners for holding the unit together.
In the case of many popular fence styles where a privacy fence that is six feet high or more is desired, it has been found desirable to use three horizontal rails, which also provide a changing pattern for decorative purposes.
Another problem that has been encountered is the method of attaching horizontal boards or rails to the posts. While in some cases the horizontal rails or boards may be simply fastened to the side of the post with bolts that go all the way through the post, this has been considered to be an unattractive arrangement, and there has been a tendency to use hollow posts with openings in the sides shaped to receive the boards or rails which then must be longer in length than the space between adjacent post sides. This arrangement makes it difficult to use a central core to stiffen the post, and therefore, it does not give strong support for the horizontal fence members. Not only do the openings in the side walls of the post weaken the post, but the load must be taken edgewise on the bottom of the openings. Furthermore, unless additional fasteners are used, the horizontal rails or boards must be a relatively loose fit in the openings, which does not result in a tight structure.